1. Field of the Invention
This invention relates to a coating composition and to a combined sizing and coating composition for glass fibers and more particularly to an aqueous coating and combined sizing and coating composition that includes a zinc salt complexed with ammonia for coating glass fibers for use in reinforcing elastomeric products.
2. Description of the Prior Art
It has long been recognized that glass fiber material should make an ideal reinforcement for automobile tires (U.S. Pat. No. 2,184,326), rubber timing belts (U.S. Pat. No. 2,135,057) and other elastomeric products. In preparing glass fiber materials for such application, individual glass fibers and groups of glass fibers in the form of strands, roving, fabric, and the like are coated with a rubber adhesive to aid in bonding of the glass to the elastomeric material to be reinforced. By far, the most widely used adhesive for preparing glass fibers for reinforcing rubber or rubber-like material is resorcinol-formaldehyde resin. The resorcinol-formaldehyde resin is generally applied to glass fiber material prior to molding of the reinforced elastomeric article by contacting a glass fabric or the like with an aqueous mixture having the resin dispersed therein. The aqueous mixture usually includes, in addition to resorcinol-formaldehyde resin, an elastomeric latex selected from natural and synthetic latices, since it is known that the incorporation of such latices into a rubber adhesive mixture aids in the bonding of the glass fiber material coated with such mixtures to the elastomeric material to be reinforced.
Largely because of its high cost, a satisfactory substitute for all or part of the resorcinol-formaldehyde resin has long been sought. Additionally, the resorcinol-formaldehyde resin is difficult to apply to the glass fiber material in a manner whereby the resin may thoroughly impregnate the fabric to coat the glass fibers forming the fabric. Therefore, often uncoated glass fibers remain in the fabric after being contacted with the resinous mixture. The strands, of course, are subject to glass-on-glass abrasion which can soon destroy the long strands of glass in a fabric and render its reinforcing properties unsatisfactory. In applying conventional resorcinol-formaldehyde containing aqueous coating compositions to glass fibers by conventional techniques such as a roller applicator described in U.S. Pat. No. 2,873,718, it has been found difficult to obtain in a single application, a coating of sufficient weight. That is, it is known that glass fiber material should realize a weight gain of at least about 15-20% and preferably about 25-30% by weight based upon dry glass for best results in reinforcing elastomeric compositions. Conventional resorcinol-formaldehyde mixtures, as applied to glass fiber materials, build to the desired coating weight only with difficulty, for example, as by increasing considerably contact time with the roller. Additionally, much of the coating may actually be squeezed off by the roller applicator, presumably due to the mixture's low viscosity and the tension exerted on the fibers.
U.S. Pat. No. 3,718,448 "Glass Fiber Forming and Coating Process" by Warren W. Drummond and Donald W. Denniston and assigned to the assignee of this invention, discloses apparatus for applying a combined sizing and coating composition to individual glass fibers and then drying the fibers in strands and collecting the dried strands on a forming tube. By this process the glass fibers are simultaneously coated with both the sizing and the coating in a single coating step that reduces substantially the time and equipment required to process the glass fibers for use as a reinforcement in elastomeric products. The combined sizing and coating compositions previously employed with this process included only resorcinol-formaldehyde as the resin constituent.
There is a need, therefore, for a combined sizing and coating composition that may be more economically prepared and applied to the glass fibers as a single coating.